On 15/10/20 10:49 +0000, Juraj Linkeš wrote: > Hi dpdk devs, > > Is there a constraint on how low RTE_MAX_LCORE can be? I'm implementing a > discovery mechanism that sets RTE_MAX_LCORE according to the number of host > cores, but I'm hitting errors when the values are low: > https://travis-ci.com/github/jlinkes/dpdk/jobs/399596828 > Message: Found 2 > cores > Message: Found 1 > numa nodes > > ../app/test/test_rcu_qsbr.c:296:54: error: iteration 2 invokes undefined > behavior [-Werror=aggressive-loop-optimizations] > > ../app/test/test_rcu_qsbr.c:315:55: error: array subscript is above array > bounds [-Werror=array-bounds] > > All VM jobs failed in that Travis build. Travis VMs only have 2 cores, so I > tried to put a bound on the build. I set it to 4 and all jobs except GCC > shared lib jobs passed, which still threw iteration 4 invokes undefined > behavior error: > https://travis-ci.com/github/jlinkes/dpdk/jobs/400004089 > > ../examples/performance-thread/l3fwd-thread/main.c:2338:34: error: iteration > 4 invokes undefined behavior [-Werror=aggressive-loop-optimizations] > > This happens for number of cores < 32 and looks like a limitation unique to > l3fwd (with cores between 4 and 32 - I didn't see the error elsewhere). > > Should I use the bound or are these legitimate errors? The fact that only GCC > (and not clang) shared lib jobs failed is also suspicious. > > Thanks, > Juraj >
Hi, I can see a CPU config setting it to 4, so it might be a valid value. Not sure it would be the lower bound though. However, I think the issue you get here shows why your discovery mechanism is not great. Most of the time, DPDK applications are not built on their target machine: either due to CI (like your issue), automatic packaging, cross-compilation for smartNIC, etc. Platforms that would benefit from your discovery mechanism will define RTE_MAX_LCORE explicitly, e.g. in config/arm/meson.build, line 34 and further. Regards, -- Gaëtan
